Manual browser: swwdog(4)

SWWDOG(4) Kernel Interfaces Manual SWWDOG(4)


swwdogsoftware watchdog timer


pseudo-device swwdog


The swwdog driver provides a software watchdog timer that works with wdogctl(8). If the timer expires, the system reboots if the boolean variable swwdog_reboot is true; otherwise, the system will panic. swwdog_reboot is accessible as a sysctl(8) variable, hw.swwdog.reboot and defaults to false.

The default period of swwdog is 60 seconds.

As with other watchdog timers, the swwdog driver prevents a system from suspending when the watchdog is armed.


The swwdog driver was written by Steven M. Bellovin.


Only one watchdog timer can be active at any given time. (Arguably, this is a bug in the watchdog timer framework.) Therefore, only a single instance of the swwdog device can be created.

Kernel tickle mode is useless with swwdog and arguably should be rejected, since both it and this driver rely on the same callout mechanism; if one is blocked, almost certainly the other is as well.

The alarm option to wdogctl(8) isn't implemented.

June 8, 2011 NetBSD 7.0